lifeguard
n. countablen. a person whose job is to watch swimmers at a beach or pool and rescue them if they are in danger. They also make sure everyone follows the safety rules.
n. an expert swimmer employed to supervise bathers at a beach or pool, preventing accidents and performing rescues when necessary.
The lifeguard blew her whistle when the boy ran near the pool.
Every summer, the city hires a certified lifeguard to monitor the public beach and provide first aid to visitors.
While the primary duty of a lifeguard is to intervene during active drownings, much of their time is spent on preventative measures like identifying dangerous rip currents or enforcing diving restrictions.
From life + guard, calque of Dutch lijfgarde, where life has the sense of Dutch lijf (“body”) (hence literally “bodyguard”). Compare German Leibgarde (“bodyguard”), Danish livgarde (“bodyguard”), Swedish livgarde (“bodyguard”). Compare also Old English līfweard (“guardian of life”).